waht is Linen Panel?

Answer 1

The phrase usually refers to late medieval/ early modern fashion for relief carving wooden panels to resemble a stylistic rendering of a piece of fabric folded on them. Some time called "parchment fold" These were commonly used on paneled walls and in chests and other "panel and stile" furniture. Goggle them.

The other possibility of your question is a piece of actual linen or cotten canvas glued to a wooden support to paint on. I could not tell from the question.